1. Field of the Invention
This invention relates in general to a bearing structure, in particular to a bearing structure used for supporting an end of a lightweight axis, such as a shaft of a pointer of a tachometer or speedmeter or the like, rotated by light torque.
2. Description of the Prior Art
In a bearing which supports a lightweight axis, such as a pointer of a tachometer or speedmeter, rotated by light torque, it is not required to have mechanical strength in a structure in itself and a fixing structure of the bearing. On the other hand, however, the bearing has to have a function that can be adjusted toward the axial direction of the axis accurately so as to meet the position of the axis. Further, once the position is decided, it is required to fix the bearing such that the position of the axis is not displaced.
In a bearing structure having the bearing which can satisfy the above requirement, the structures as illustrated in FIGS. 1 and 2 were conventionally adopted.
FIG. 1 is a section view showing the position that such a bearing structure is actually used in a meter. In FIG. 1, a numeral 1 indicates a housing of the meter. On the housing 1, an upper plate 2 is provided. Said upper plate 2 has an aperture in its central portion, and a bearing structure 3 is mounted in the aperture. Said bearing structure 3 supports an axis 4 rotationally which is rotated in accordance with rotation of a drive shaft (not shown). On top of the axis 4, a pointer 5 is attached. In the drawing, a numeral 6 indicates a scale plate.
FIG. 2 is an enlarged view showing the bearing structure 3. In the drawing, the numeral 10 indicates a bearing support which consists of a metal such as brass or aluminum. The bearing support 10 comprises a cylindrical portion 10a and a flange portion 10b. On a part of an outer surface of the cylindrical portion 10a of the bearing support 10 and on an inner surface thereof, there are formed an external thread 10c and an internal thread 10d, respectively. The bearing support 10 is fixed to the upper plate 2 by inserting the cylindrical portion 10a of the bearing support 10 into an aperture of the upper plate 2 and fastening a nut 11 onto the external thread 10c of the cylindrical portion 10a.
Into the cylindrical portion 10a of the bearing support 10, a bearing 12 which also consists of a metal material is mounted. The bearing 12 also comprises a cylindrical portion 12a and flange portion 12b. On the outer surface of the cylindrical portion 12a, an external thread 12c which is threaded with the internal thread 10d of the bearing support 10 is formed.
In order to adjust the position of the bearing 12 with respect to the position of an axis 4 finely, the bearing 12 is turned clockwise or counterclockwise. After the adjustment is completed, the bearing 12 is fixed to the bearing support 10 with an adhesive 13. As a result, the bearing 12 is fixed to the bearing support 10 secured to the upper plate 2 and can maintain the adjusted position without displacing therefrom.
FIG. 3 illustrates the other conventional bering structure. This structure comprises a bearing support 20 and a bearing 21 both consisting of a metal such as brass or aluminum. The bearing support 20 has a cylindrical portion 20a and flange portion 20b. In an inner surface of the cylindrical portion 20a, there is formed an internal thread 20c. A bearing 21 which supports an axis 4 rotationally and around which an external thread 21a is formed is screwed into the internal thread 20c of the bearing support 20. The cylindrical portion 20a of the bearing support 20 is inserted into an aperture provided in the upper plate 2 and a nut 22 is screwed onto the external thread 21a of the bearing 21. In the conventional structure, in the same manner as that of the conventional structure in FIG. 2, after the position of the bearing 21 is finely adjusted, the bearing 21 is fixed of the position by fastening force between the nut 22 and the bearing support 20.
As appeared from the conventional structures, the bearings 12 and 21 have the following two functions. One of the functions is a beaaring function which supports the axis rotationally, and the other is an adjusting function which finely adjusts the position of the axis with respect to the bearing 12 or 21 and fix the position of the bearing. In both conventional structures, the fine adjustment of the bearing is performed by screwing the bearing 12 or 21. On the other hand, the positioning of the bearing 12 or 21 is performed by the adhesion with the adhesive in the structure in FIG. 1, while in the structure in FIG. 2 a double nut fastening is used as the positioning.
However, the conventional bearing structures have the following disadvantages, respectively. Specifically, in the former structure that the adhesive is used, according to the amount of the adhesive applied thereon, a dispersion of fixing strength is apt to be caused. As a result, if the amount of the adhesive is little the fixing force is deteriorated and further if the application of the adhesive is forgotten the fixing position of the bearing may be displaced.
In addition, if an oleo-resin or a flourine-containing resin is used for materials of the bearing, there is a case that the adhesive can not be used, to that the materials used for manufacturing of the bearing is limited.
Further, in the bearing structure that the double nuts fastening is used or the structure that the adhesive is used, as shown in FIGS. 2 and 3, screwing operations have to be done between the bearing support 10 or 20 and bearing 12 or 21, and between the bearing support 10 or 20 and nut 11 or 22. Therefore, there is a problem that assembly thereof was very troublesome due to the necessity of the screwing operations. Furthermore, it is difficult to reduce the number of the parts more than this.
However, in order to reduce the manufacturing cost of the product, it is necessary to reduce the number of the parts as much as possible and shorten the time required for the assembly of the parts.